Specifically, the main role of on-board diagnostic systems—or OBD systems—is to evaluate the hardware operation of vehicles, and they have the ability to diagnose the presence of a fault on a propulsion component of the vehicle. OBD systems therefore consist of a set of hardware and software means, making it possible to perform hardware diagnoses targeted at the engine of vehicles.
The subject of the present invention relates to the improvement of the operation of such OBD systems, for the purpose of optimizing the accuracy of the diagnoses performed and the number of times said diagnoses will be performed.
In a known manner, OBD systems hinge on on-board computers implementing methods for monitoring or observing components of the engine, for the purpose of carrying out the most relevant possible fault diagnoses.
In practice, when a malfunction occurs on a vehicle engine, the dedicated computer detects the presence of a fault, and the vehicle has to be taken to a specialist technician for the latter to carry out investigations. First of all, the specialist technician will connect a computer (termed ‘diagnostic tool’ or ‘scan tool’) to a special socket provided on the vehicle, generally called OBD socket, and execute, by way of software means, a method having a plurality of monitoring or observation strategies that are each able to process a plurality of components, for the purpose of performing the correct diagnosis, consisting in identifying the component responsible for the malfunction. Moreover, in practice, the same ‘diagnostic tool’ enables the competent authorities to monitor the efficiency of the vehicle's anti-pollution system.
In this context, a vital parameter for the purpose of analyzing the operation of the engine monitoring is based on the knowledge of a ratio, in particular referenced using the acronyms RBM for ‘rate-based monitoring’ or IUPR for ‘in-use performance ratio’.
This ratio corresponds to the ratio between the number of times a given on-board hardware diagnosis is performed and the number of running cycles of the vehicle under consideration.
In most countries, legislation imposes that this ratio is higher than a predetermined threshold, so as to ensure, for reasons of reliability or to meet pollution minimization standards, that the engine is operating correctly by way of sufficiently frequent on-board hardware diagnoses. Depending on the hardware component under consideration, the predetermined threshold that the ratio has to exceed may vary. For example, it may be required for this ratio to be higher than 25%.
Now, moreover, in order to be relevant, the on-board hardware diagnoses may be performed only under certain conditions that are typically linked to the state of the vehicle, such as the temperature of the catalytic converter (is it hot enough?) or the engine speed (is it in fact between a certain minimum value and a certain maximum value?). Thus, some diagnoses, depending on the use of the vehicle, may be performed too infrequently, for example because said vehicle makes only small journeys at low speed, preventing the conditions for performing a given diagnosis, which conditions stipulate the requirement for the vehicle to be traveling at a relatively high speed for a certain duration, from being fulfilled.
It should furthermore be noted that particular attention is paid to any fault that may occur on components that are liable to bring about a risk of excess pollution.
Specifically, on-board diagnoses have generally become gradually more and more sophisticated, in particular so as to enable engines to comply with increasingly stringent legal polluting emissions thresholds.
Thus, complex legal requirements nowadays apply to motor vehicles, relating both to polluting emissions thresholds and methods and means to be implemented in order to detect any fault in the ability to control these emissions and to alert the user thereto.
These increasingly stringent legal requirements make optimum operation of OBD systems vital.
It should moreover be noted that there is a conflict between the desire to increase the number of times the diagnoses are performed, for the purpose of complying with the minimum RBM ratios, and the desire to perform accurate diagnoses. Specifically, if the conditions for performing a diagnosis are relaxed, the accuracy thereof is generally jeopardized. For example, some diagnoses may require the engine of the vehicle to be sufficiently hot. Now, if said vehicle makes only very short journeys, the temperature of its engine perhaps never reaches the high temperature required to perform said diagnosis. If a different calibration of the OBD system is implemented, so as to reduce the temperature threshold required for the diagnosis to be performed, said diagnosis will certainly be performed more often, but this will be to the detriment of the accuracy of said diagnosis, the latter being more accurate when the engine is hotter.
In an attempt to improve the ratio of the number of diagnoses performed to the number of running cycles of the vehicle, various methods have been developed. For example, document US 20120072060 A1, which is incorporated by reference proposes a method for monitoring an OBD system that makes it possible to identify the existence of an excessively low ratio and act, where appropriate, on the engine, so as to create the conditions for performing diagnoses.
In doing so, in the prior art, some hybrid vehicle OBD systems force the combustion engine to operate, while operation using electric power supplied by the battery is possible and less polluting, just to enable on-board hardware diagnoses to be performed on said combustion engine.